1. Field of the Invention
The present invention relates to a zoom lens, and an image pickup apparatus having the same, and particularly relates to a zoom lens which is suitable for a broadcasting television camera, a cinema camera, a video camera, a digital still camera, a silver-halide film camera and the like.
2. Description of the Related Art
In recent years, an image pickup apparatus such as a television camera, a cinema camera, a photographic camera and a video camera has been desired to be provided with a zoom lens which has a reduced size and weight, a wide angle of view and a high optical performance. An image pickup device such as CCD or CMOS which is used in a television/cinema camera as a moving image photographing system for professionals, in particular, has an almost even resolving power over the whole imaging range. Owing to this, the zoom lens to be used with such a device is required to have an almost even resolving power from the center of a screen to the periphery of the screen. In addition, reduction in size and weight is also required for a photographic style in which mobility and operability are regarded as important.
On the other hand, a wide angle lens having a short focal length at a wide angle end allows for photography over a wide range and enhanced perspective. Users who desire to use the photographic effect strongly demand a zoom lens that has a wider angle of view, a further reduced size and weight and a higher optical performance.
A negative-lead type of four-unit zoom lens is known as a wide-angle zoom lens, which has a lens unit having a negative refractive power arranged on the side closest to the object, and includes four lens units as a whole.
For instance, Japanese Patent Application Laid-Open No. H05-297276 discloses a four-unit zoom lens which has an F-number of approximately 2.0 at a wide angle end, an angle of view of approximately 60 degrees to 65 degrees at a wide angle end, an angle of view of approximately 14 degrees to 17 degrees at a telephoto end, and a zoom ratio of approximately 3.8. In addition, Japanese Patent Application Laid-Open No. H04-051006 discloses a four-unit zoom lens which has an F-number of approximately 1.5 to 2.2 at a wide angle end, an angle of view of approximately 50 degrees to 60 degrees at a wide angle end, an angle of view of approximately 8 degrees to 11 degrees at a telephoto end, and a zoom ratio of approximately 6. Japanese Patent Application Laid-Open No. S63-281113 discloses a four-unit zoom lens which has an F-number of approximately 1.8 at a wide angle end, an angle of view of approximately 80 degrees at a wide angle end, an angle of view of approximately 24 degrees at a telephoto end, and a zoom ratio of approximately 3.9. Any zoom lens includes, in order from the object side to the image side: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; a third lens unit having a negative refractive power; and a fourth lens unit having a positive refractive power.
However, in the zoom lenses which are disclosed in Japanese Patent Application Laid-Open No. H05-297276, Japanese Patent Application Laid-Open No. H04-051006 and Japanese Patent Application Laid-Open No. S63-281113, the refractive power and the lens configuration of each of the lens units are disadvantageous for further widening of the angle of view, and it becomes difficult to suppress the enlargement of a lens diameter resulting from the widening of the angle of view. When the angle of view at the wide angle end exceeds 80 degrees, in particular, the lens diameter tends to be remarkably enlarged.